Earth resistance measurements in urban contexts: Problems and possible solutions

Both EN 50522 and IEEE Std. 81 propose the Fall of Potential Method (FPM) to carry out the measurement of the resistance to earth of an Earthing System (ES). However, in urban areas, the recommended distances between the ES and auxiliary electrodes are not easy to respect, due to the presence of buildings and tarmac. Moreover, unknown buried metallic parts, as well as the interconnection among the ESs made by the Distributor System Operator, could modify the earth potential profile of the area, affecting the measurement results. In this paper, the issues that could affect the measurement result if FPM is used in an urban context are presented. A parametric analysis, carried out with Comsol Multiphysics, quantifies the errors due to wrong positioning of the auxiliary electrodes with reference to the ES under test. In addition, a field measurement is described, emphasizing the main aspects that could compromise the results. Finally, practical suggestions to reduce errors are provided

Energy Hub Model for the Massive Adoption of Hydrogen in Power Systems

A promising energy carrier and storage solution for integrating renewable energies into  the power grid currently being investigated is hydrogen produced via electrolysis. It already serves  various purposes, but it might also enable the development of hydrogen-based electricity storage  systems made up of electrolyzers, hydrogen storage systems, and generators (fuel cells or engines).  The adoption of hydrogen-based technologies is strictly linked to the electrification of end uses and  to multicarrier energy grids. This study introduces a generic method to integrate and optimize the  sizing and operation phases of hydrogen-based power systems using an energy hub optimization  model, which can manage and coordinate multiple energy carriers and equipment. Furthermore,  the uncertainty related to renewables and final demands was carefully assessed. A case study on an  urban microgrid with high hydrogen demand for mobility demonstrates the method’s applicability,  showing how the multi-objective optimization of hydrogen-based power systems can reduce total  costs, primary energy demand, and carbon equivalent emissions for both power grids and mobility  down to −145%. Furthermore, the adoption of the uncertainty assessment can give additional  benefits, allowing a downsizing of the equipment.&nbsp

A parametric study on unbalanced three phase islanded microgrids with inverter interfaced units

In this paper, the solution of the power flow for unbalanced three phase microgrids systems is proposed. The study aims at the integration of inverter interfaced units using the control law used for primary voltage and frequency regulation, so as to take into account possible small variations of these parameters to account for sudden load changes. The proposed study deals with unbalanced systems which is the typical case of small distribution systems and shows how the power losses term varies as the regulators parameters vary as well, thus showing that these are sensitive parameters that could have an important role in optimal management of such system

Optimal Power Flow in three-phase islanded microgrids with inverter interfaced units

In this paper, the solution of the optimal power flow (OPF) problem for three phase islanded microgrids is studied, the OPF being one of the core functions of the tertiary regulation level for an AC islanded microgrid with a hierarchical control architecture. The study also aims at evaluating the contextual adjustment of the droop parameters used for primary voltage and frequency regulation of inverter interfaced units. The output of the OPF provides an iso-frequential operating point for all the generation units and a set of droop parameters for primary regulation. In this way, secondary regulation can be neglected in the considered hierarchical control structure. The application section provides the solution of the OPF problem over networks of different sizes and a stability analysis of the microgrid system using the optimized droop parameters, thus giving rise to the optimized management of the system with a new hierarchical control architecture

Fall of Potential Measurement of the Earth Resistance in Urban Environments: Accuracy Evaluation

Both Standards EN 50522 and IEEE 81 propose the Fall of Potential Method (FPM) to carry out the measurement of the Resistance to Earth (RES) of an Earthing System (ES). However, in urban areas, the recommended distances between the ES and auxiliary electrodes are not easy to respect, due to the presence of buildings and tarmac. Furthermore, unknown buried metallic parts and interconnections among ESs could modify the earth potential profile of the area, affecting the measurement results. In this paper, the key-issues that influence the measured RES when the FPM is used in an urban environment are presented. A parametric analysis, carried out with Comsol Multiphysics, quantifies the errors due to wrong positioning of the auxiliary electrodes and due to the presence of interconnected ESs in the proximity of the ES under test. In addition, a real case of field measurement is described, emphasizing the main aspects that could compromise the results. Finally, practical suggestions to reduce errors are provided

Critical Assessment of Feed-In Tariffs and Solar Photovoltaic Development in Vietnam

Vietnam became the world’s third largest market for solar photovoltaic energy in 2020. Especially after the Vietnamese government issued feed-in tariffs for grid-connected solar photovoltaic systems, the installed capacity of solar photovoltaic applications exploded in 2019. From studies carried out in the relevant literature, it can be said that support policies are highly important for the initial development of the renewable energy industry in most countries. This is especially true in emerging countries such as Vietnam. This paper reviews the feed-in tariffs issued and deployed in different regions of Vietnam for grid-connected solar photovoltaic applications. Moreover, the paper takes a closer look at the costs of electricity production from these systems in relation to the feed-in tariffs issued in Vietnam. The results show that the gap between the levelized cost of electricity and the feed-in tariff for solar photovoltaic electricity is relatively high, particularly in regions with a lower irradiation potential